Re: discussion over usb-serial

On Mon, Jan 29, 2007 at 09:36:58AM +0100, Nathael Pajani wrote:
> Hi !
> 
> I agree with you on all the points, but then, I cannot do what I want, as 
> this
> job is for a customer.
> 
> Greg KH a wrote :
> >On Thu, Jan 25, 2007 at 10:25:34AM +0100, Nathael Pajani wrote:
> >Don't use the generic driver for any real device, it's not made for that
> >at all.
> That's what the customer is actually doing, and what is found at the end of 
> the
> documentation: Documentation/usb/usb-serial.txt
> Generic Serial driver
> 	insmod usbserial vendor=0x#### product=0x####

Yes, that's a good way to get some devices up and running with no kernel
changes.  But to do it "correct" a kernel driver needs to be written.
This driver can be very tiny, as some of the usb-serial drivers show.

> >>So I'm "writting" a "fake" driver, which uses most of the generic one, 
> >>but is not the generic one.
> >
> >You can do that in very few lines, look at the funsoft.c driver for such
> >an example.  I recommend doing that.
> That's what my driver looks like, whith only probe and disconnect functions 
> for some stuff.

That's great.

> >>Why don't I simply modify the generic driver ?
> >
> >Because I will not let you :)
> Of course :)
> But this is for a customer with very particular needs, not for the 
> mainstream kernel.

Ok, but it would probably be good to get your "paticular" kernel module
in the main tree so you don't have to maintain it over time...

> >>Because I need other functionnalities like "static" allocation of tty 
> >>numbers (just think of the number of cables connected to the PC, and try 
> >>to immagine yourself trying to find which ttyUSB is which device....)
> >
> >That's what sysfs and udev solve.
> Partly, but the customer does not want udev.

Then just look at sysfs for the links.

> And I do not see which part in the usb-serial code makes device connected to
> port 18 on the machine be ttyUSB18 if it's the first connected device.
> It would be ttyUSB0. no?

What does "first connected device" mean?  It can mean one thing this
boot, another thing the next boot :)

> Maybe I'm missing something, I'm not accustomed to udev, just told the 
> client that we should have a look at it for it may solve some parts of
> his problem and he told me he does not want udev, so I did not look
> further.

If he wants to name these devices in a way that will always be the same,
no matter what happens on boot, you need to do something like what udev
does.  That is what it was created for.

> >Care to post what you have?
> This would be no problem,
> If you want I can send it all to you in the end, just ask me.
> This is GPL code isn't it ?

It sure should be :)

So sure, please post it.

thanks,

greg k-h

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